Current Events In this article, scientists have discovered that a competitor with two prosthetic lower legs are outrunning the competition because the prosthetics make him run "15-20% faster, equal to 10 seconds over a 400 meter race, than he otherwise would be with natural legs." The reason for this is because regular bone density weighs more than half of a prosthetic, which changes the runner's ability to run faster than someone with natural legs possibly can.
What Do You See? There is a kid in a red shirt running and kicking the ball over the goal. Another kid is standing still while kicking a ball, and it doesn't get enough momentum to get a good distance.
What Do You Think? Once they begin to slide across the ice, they gain momentum and that keeps them at high speeds while no large effort is made to do so. The soccer ball that has been kicked across still has force and momentum, which keeps the acceleration going.
Investigate 2A) 5.25 m 2B) The skater will go back and forth but will graduallydecrease his height as time goes goes on.
3A) The result was 6.03 m. The prediction wasn't completely off, but it was close. Also as time went on, the height of the skater did not decrease or increase. 3B) The ball remains constant in its maximum height.
4A) Our prediction is that, the maximum height of the ball will be less than its maximum height with a steeper slope. Measurement prediction: 5.50 m. 4B) The result is 5.08 m. Our prediction was very close because we predicted the maximum slope to be less than when it had a steep slope. The second result is 4.41 m. Still proving our prediction to be correct.
5A) No because there is no slope to give the skater the necessary momentum to bring him back to max height. He will simply fall of the slope. 5B) We predict it will take 100 m. for the skater to stop. 5C) The thing to keep the skater rolling on the track is to have absolutely no friction to allow him to stop. 5D) The skater does not stop rolling no matter how long the horizontal track is.
6A) The other side of the track is elongated. 6B) The max height also decreases with a less steep slope. 6C) They are usually about equal if the slope on each side is equal. 6D) The skate would not stop if there was a horizontal slope. If there was not a horizontal slope, he would go back in the other direction.
Physics Talk, p134-138 Inertia:the natural tendency of an object to remain at rest or to remain moving with constant speed. Force: a push or a pull Newton's First Law: in the absence of an unbalanced force, an object at rest remains at rest, and an object already in motion remains in motion with constant speed in a straight-line path. Mass: the amount of matter in an object; how we measure inertia; measured in kilograms Weight: how much gravity pulls on a mass Speed: the charge in distance per unit of time Velocity: speed in a given direction Acceleration: the change in velocity per unit of time Frame of Reference: a vantage point with respect to which position and motion may be described.
Checking Up, p138
Inertia is a property of matter that measures the resistance to changes in an object's motion.
Things won't change their motion unless they are forced to.
Friction
Friction
Greater mass
Relative to the train
What Do You Think Now? Both the figure skater and soccer ball will continue to roll on a horizontal plane until the object reacts with friction. Their speed is determined by the amount of friction; both will lose their speed with more friction, and increase their speed with less friction. Theoretically, they can continue for ever if there was no friction to stop them.
Physics To Go, p143 1) It will never stop because there is no unbalanced force to do so.
2) It reaches the same height that it started with as long as there is no friction (20).
3) No because everything has at least a little but of friction.
4) The puck will glide at constant speed.
5) 2.5 m/s + 4.5 m/s = 7 m/s
6) 4.2 m/s + 10.3 m/s = 14.5 m/s
7A) 5.6 m/s + 2.4 m/s = 8 m/s forward 7B) 5.6 m/s - 2.4 m/s = 3.2 m/s forward 7C) 5.6^2 + 2.4^2 = c^2 [square it] 6.1 m/s at 67 degrees, 23 degrees from train direction
8) 85 m/s - 18 m/s = 67 m/s
9A) 21.2 cm 9B) 43.9 cm 9C) 58 cm 9D) 172 cm
10) Bowling, punting a football, and a basketball use Newton's First Law because the ball will stop rolling at some point because outside forces are influencing it. The ball will keep rolling unless it acts against a surface with friction.
Inquiring Further Most baseball players need to beat out the ball to get to first base, and they can run through the base. However, overrunning the base allows the runner to get tagged and be out, so they need to slide and react with the friction of the ground to stop before they overrun the base.
Section 2
What Do You See? In the top section of the picture, the boy is walking slowly and is footprints are closer together; at the bottom half, he is sprinting after a girl with flowers in tow, and his footprints are much further apart.
What Do You Think? The meaning of 100 mi/h = 45 m/s. The number for distance is significantly less because of the conversion between miles and meters, and hours and seconds.
Investigate See group wiki
Physics Talk, p148-151 Acceleration: a change in velocity of an object over time
a = delta v / delta t
Average Speed: the distance traveled divided by the time it took to travel that distance
v(av) = delta d / delta t
Instantaneous Speed: the speed measured during an instant: the speed as the time interval approaches, but does not become zero.
Checking Up, p151 1A) The dots have a constant pattern and similar separation between each dot. 1B) The dots start out close together and then begin to grow apart in distance 1C) The dots start out further apart and move closer together. 2) 400m / 50s = 8 m/s 3) Instantaneous speed is the speed one is traveling at that exact time, compared to average speed which is the average speed over the course of a period of time. 4) v = 3.6 km/s , t = 10 s 3.6 / 10 = .36 km/s
Physics Plus, p152 1)
Velocity
Acceleration
Example
Small
Small
Turtle
Big
Big
Rocket
Small
Big
Rabbit, Dog, Deer *rebounding (any object)
Big
Small
Truck
Rebounding: changed direction. Even if the speeds are small, accelerations can be huge if the bounce times are tiny.
2) a = vf - vi / t -.5 m/s - .5 m/s/ .2 s a = -5
3A) .5 m/s 3B) -0.5 m/s 3C) .5 m/s
What Do You Think Now, p152 The miles still need to be converted into meters, as well as changing the hours to correspond with seconds, which is converted into 89.7 m/s. Distances traveled in comparison to time usually go hand in hand. In this example, every hour 100 miles have been completed, compared to 45 m/s, which is 45 meters per one second. By an hour, 162,000 meters will have been covered.
Physics To Go, p154-156 1) Average speed 2A) 60 m/s 2B) 14 m/s 2C) 4.8 km/h 2D) 89 km/h 3A) negative acceleration 3B) positive acceleration 3C) constant speed 3D) negative 3E) constant speed 3F) constant speed 4A) A & D 4B) B 4C) A 4D) C 4E)
A - +
B - 0
C - +/-
D - +
6A) a = vf - vi / t 0-12.5 m/s / 9 s = -1.4 m/s 6B) negative
8) 100 m / 2 h = 50 mph 9) No because the speed will almost never be maintained. They may have walked very fast for the first few blocks and slower for the rest. 10) See chart 11) 4 m/s x 5 s = 20 m/s
14A) When running track, you are in constant motion but your speed may begin to vary the longer you're running for. 14B) When pitching a softball, you wind up to get the ball to move faster in order for it to constantly accelerate at a fast speed. 14C) When bowling, the ball is moving pretty slowly at a constant speed. 14D) When running to pole vault, you need to have a running start before putting the pole down to ensure that you go straight up in the air. 14E) When running to 2nd base, you need to slow down in order to not overrun the base.
Section 3
What Do You See? The girl is walking with a red stick, pushing a blue ball. When she increases her speed, it's difficult for her to continue to push the ball because she is hindered by the red stick's friction to he ground. The more she pushes, the higher she goes.
What Do You Think? Force is a push or a pull exerted onto an object. A tennis ball will have more force exerted onto it than a bowling ball based on its smaller mass, which allows the tennis ball to move further away than the bowling ball at a faster speed.
Investigation See Group Wiki
Physics Talk, p161-167 Free-Body Diagram: a diagram showing the forces acting on an object Weight: the vertical, downward force exerted on a mass as a result of gravity Equation for Newton's Seond Law of Motion
acceleration = force / mass
a = f / m
Class Notes With an unbalanced force, an object will acclerate. Newton's Second Law: Net force is directly proportional to acceleration. Gravity = 9.8 m/s^2
F(net) = mass x acceleration
A = f / m
W = mass x gravity
F = mass / acceleration
F(gravity) = m / a(gravity)
A = mass(b) x gravity / mass(a) + mass(b)
A big force causes a big acceleration; a small force causes a small acceleration. A big mass needs a big force to accelerate; a small mass needs a small force to accelerate
F is proportional to a
A is proportional to 1/m
F is proportional to m
Net force has NO RELATIONSHIP to velocity
Checking Up, p167 1) Newton's Second Law: Net force is directly proportional to acceleration 2) The acceleration will be increasing even with a constant force. 3) You would need to work backwards to find how much it weighs in pounds:
weight in N = mg (x kg) x 9.8 = 30 N x = 3.06 kg
y lbs
_ = 3.06 kg
2.2 kg
y = 6.732 lbs z = 30 N
4) Your mass will remain the same, but your weight would change because of the gravitational force that your body has on that planet.
Physics Plus, p169
What Do You Think Now, p170 After finishing the Investigation, now I know the exact formula for calculating force in association with mass and acceleration. Due to Newton's Second Law, force is exerted onto an object, and a greater mass increases its speed.
Physics to Go, p171-173 1)
3) a = ? m = .3 kg F = 42 N
42 N = (.3 kg) a a = 140 m/s^2
4) f = ? m = .04 kg a = 20 m/s^2
f = (.04 kg) 20 m/s^2 f = .8 N
5A) The bowling ball has a greater mass and therefore a greater inertia, making it much more difficult to stop, unlike the baseball. 5B) The bowling ball and the baseball have the same force but the acceleration differs due to their mass.
9) Once the ball is released from your hand, there is no force acting on the ball except its acceleration. 10) 90 N 11) 4 x 200 = 800 N 12) 179 m/s^2 13) 130 N @ 67 degrees NE 14) 6403 N @ 39 degrees 15) 125 N
16A) 50 N @ 53 degrees 16B) 8.9 m/s^2
17A) 36 N @ 34 17B) .36 m/s^2 17C) .5 m/s^2
18) Welcome to the Pascack Hills Volleyball State Tournament Finals! The home team, Pascack Hills, seed 4, is playing against the number one seed, Old Tappan. Aiyana Whitney smashes the ball down at a velocity of 2.5 m/s. Her 6 foot 3 inch stature gives the spike an edge, yet libero Keira Eichenlaub manages to put the ball back up. Sam Kurtzke, the setter, sprints to the ball to set it up to Jess Holm. Taking her approach, Holm sets herself up to increase her velocity to impact upon the ball, and her arm swing gives more speed to the balls initial velocity. The OT girls react too late, and Pascack Hills wins the point!
Section 4
What Do You See? A girl is on a ladder dropping a red apple in free-fall, and the green apple is projecting. The two headed guy is timing both apples.
What Do You Think? Both weight and velocity affect how far a thrown object travels.
Investigation See Group Wiki (Group III)
Physics Talk Trajectory: path Projectile: an object acted on ONLY by gravity
The x-component and the y-component of all vectors are independent
Vertical velocity affects vertical distance
Horizontal distance affects horizontal distance.
Time for a projectile to reach the ground (hang time) is the same as the time it takes to drop
Acceleration due to gravity is -9.8 m/s^2
Gravity is always negative
Vertical velocity changes by -10 m/s every second
Horizontal velocity does not change ever
Throwing horizontally results in the same trajectory as the second half of the path of the ball thrown at an angle.
Checking Up 1) They dropped at the same height, and acceleration is acting on both of them. 2) It increases about 10 meters every second 3) Velocity is 0 m/s; Acceleration is -9.8 m/s^2
Physics Plus, p179 1) 2) 
What Do You Think Now? After completing the Investigation, I now know that the height of the ball, the speed at which the ball is thrown, and the angle at which the ball is thrown affects the distance.
Physics To Go 1-2) 4) d=1/2at^2 6) This is true because the x and y components are independent; vertical distance is only affected by verticals, and horizontal distance is affected by horizontals. 7) Both of them hit the ground at the same time because the vertical component is the same but not the horizontal. 8) 36 @ 33.7 degrees 9A) 11.98 m/s 9B) v=d/t 11.3=d/t d=23.96 10A) 8.5 m/s 10B) 4.25 m/s 11) Sammi Panso steps up to the plate, preparing for the fury Meredith Hryzck is about to release from the pitcher's mound. Hryzck winds up windmill style, and wow! Look at that! 80 miles an hour! The ball is spinning so much yet moving seamlessly on an imaginary horizontal plane; there's not way Panso will get this one. BAM! Gee whiz, that ball is really flying. And off she runs! (That's sure going to be at least a double, Amanda.) That's right imaginary co-anchor, the ball had some great arc on it; let's see if center fielder Ashley Worthington can manage to catch it. (Amanda, that ball is arced a little too much; I think Worthington is going to be able to catch it.) The ball is coming back to Earth now at an acceleration of -9.8 m/s^2, and Worthington is running back and back... AND SHE DIVES FOR THE BALL! Is it a catch, YES WE HAVE A CATCH. That was some play, Imaginary Co-Anchor, some play. And that's the game!
In this video, we see the players going up for spikes during their volleyball warmup. The ball is tossed up, with an initial acceleration of 0, and once it reaches its highest point, it accelerates at -9.8 m/s^2. Once the ball hits that point, the player begins their approach. This vertical motion of the ball is off set by the swinging of the arm, at which point the ball has no choice to go down. However, when the timing is off, the ball will be hit and move on a horizontal plane. The shape of the trajectory once the ball is spiked allows the opposing players to have a harder time digging the ball. If they fail to do so, the offensive team wins a point, helping them secure a win. http://www.youtube.com/watch?v=rP2_4P0gMXk
Section 5
What Do You See? A girl is kicking the ball backwards, and the ball is brought back down only to be hit off of number 2's head into the goal.
What Do You Think? Depending on the angle that the ball is kicked at, it will reach a maximum of various heights and distances along the x and y axis. If the projectile is kicked harder, the force exerted onto the object
Investigation See Group Wiki
Physics Talk, p188-189
All balls travel in parabolas
The 45 degree launch angle yields the greatest range (largest distance).
Complimentary angles have the same distance
Small angles have greater horizontal velocities but are in the air a short time.
Large angles have smaller horizontal velocities but are in the air for a long time.
Air resistance makes trajectories more complex
The temperature of the air affects the distance a ball will travel.
Checking Up, p189 1) Horizontal motion and vertical motion are the two types of motion that show the trajectory of a projectile. 2) The model must match reality in nature, which means that the model must be backed up by science as well as show the physicality of the nature being shown. 3) Because ten degrees and 80 degrees are complimentary, they will yield the same distance. The ten degree launch will have a longer horizontal velocity than the eighty degree launch, but the latter will have a much higher vertical velocity.
Physics Plus, p192
What Do You Think Now? The angles of the trajectory affect the projectile and where it moves to. When the angle is close to 45 degrees, the range is greater than if it were further away. Sometimes a projectile can be launched from a different angle yet yield the same range; angles that are complimentary (total 90 degrees) have the same range.
Physics To Go, 194-195 1) If the angles have the same range, then the angles must be complimentary. For the furthest distance, both angles must each total 45 degrees.
2A) The vertical distance will increase while the horizontal distance will decrease. 2B) The horizontal distance will increase while the vertical distance will decrease.
5) v(ix) is high and his maximum horizontal range is high.
6A) a = -g = -9.8 m/s down 6B) v(max) = v(ix) v(y) = 0 at maximum height
7A) 29.4 m/s 7B) 5 m/s 7C) 15 m/s
8) Closest to forty five degrees 9) Biggest angle, the one closest to ninety degrees
10A) Down'
10B) d = v(i) + 1/2at^2 -100 = .5 (-9.8) t^2 -200 / -9.8 = 4.5 s
10C) d(x) = v(ix)t d = 20 x 4.5 90 m
Section 6
What Do You See? A boy looks like he is pushing against the wall as if to move it with all his might, but then he is propelled backwards.
What Do You Think? They should bend their knees and push their feet into the ground, before propelling themselves upward. Gravity is pulling you down while Normal forces propel you upward.
Investigation Part A 1A) The moment force is applied. 1B) When acceleration is equal to zero, there is no unbalanced force acting upon it. 1C) The force is a push which acts in the opposite direction of where you are moving. 1D) You push in the opposite direction on the wall. 1E) Both of them are equal in magnitude because if they weren't the wall would move to push you or you would go through the wall.
2A) Student A pushes forward and moves backwards. 2B) The force of the student's hands against the other student's hands causes the motion to propel backwards. 2C) The motion of the hands of students A & B are of equal force, causing the same motion 2D) The force of the student's hands against the other student's hands causes the motion to propel backwards.
3A) The forward forces comes from the backward force of each step of the show pushing off from the floor. 3B) It is possible but because of the lack of friction, more force must be applied to each step.
4A) The force will always be equal because they have the same mass and force, only in opposite directions. 4B)
Part B 3A) The more mass that rests on the ruler creates a greater bend.
4A) With each Newton of force, there is a greater deflection in the meter stick. 4B) The deflection is greater when the weight is greater. 4C) The stick is still deflecting, but at such a small angle it cannot be seen. 4D)
Physics Talk, p201 Newton's Third Law of Motion: Forces come in pairs; the force of object A on object B is equal in strength and opposite in direction to the force of object B on object A. Free-Body Diagram: a diagram showing the forces acting on an object Center of Mass: the point at which all the mass of an object is considered to be concentrated.
Class Notes:
1) An object at rest will stay at rest, and an object in motion will stay in motion at constant speed in a straight line, unless an unbalanced force acts upon it.
2) Acceleration is directly proportional to net force and inversely proportional to the mass of the system.
3) Every action has an equal but opposite force.
Checking Up, p205 1) When two objects have equal force is opposite directions. 2) Gravity and Normal forces act against each other. 3) The free-body diagrams illustrate where each force is moving in comparison to an object.
Physics Plus 
Physics To Go, p208 1) Yes but it is equal to the opposite. 2) No but restoring forces balance weight downward. 3) A spring with a needle attached, calibrated. 4) Equal but opposite break because the force of the ball is too big for material to withstand. 5) Equal but opposite. The smaller running back has a larger acceleration but exerts the same force. 6) The forces are equal and opposite. 7) Padding causes lower acceleration which reduces force on hand.
8A) Mark Sanchez is waiting for the snap and oh no, the play clock is running out! One second left... the ball is snapped just in time. The linebackers slam into each other, exerting their own force upon their opponent. Newton's Third Law is at play, as you can see the line is not moving; equal forces are coming from both sides of the field. Meanwhile, Sanchez is looking for Dustin Keller, fakes, and bombs it to Braylon Edwards. Look at that throw, but oh no! It's too high! Edwards jumps up, catches it in mid air, and falls into the N-Zone. TOUCHDOWN NEW YORK! 8B) Deflection on the ground causes force because when an object hits the ground at one force, it will deflect with the same amount of force.
What Do You Think Now? You are pushing your weight down upon the floor, while normal forces are pushing upward. The normal forces of both yourself and the floor are equal, which allows you to spring upward.
Section 7
What Do You See? The person is pulling a shoe across the ice easily with a spring scale, but is having difficulty doing so on the sand.
What Do You Think? Certain shoes like cleats have spikes that stick into the sand or grass or turf, allowing for more traction. Athletes that wear them need to stay up while running, and the spikes allow them to do so. Other shoes like volleyball and basketball sneakers are meant so the athletes won't slip on the court and injure themselves.
Investigation 2-7 See Group Wiki
Physics Talk, p212 Friction: a force that resists relative motion between two bodies in contact Normal Force: the force acting perpendicularly or at right angles to a surface. Coefficient of sliding friction: a dimensionless quality symbolized by the Greek letter (meu); its value depends on the properties of the two surfaces in contact and is used to calculate the force of friction.
The higher the coefficient of friction, the rougher the surface
Ratio of friction over normal forces
No units
Decreasing Speed: Increased Friction
Increasing Speed: Decreased Friction
Checking Up, p214 1) They are both equal forces because on is sliding friction and the other is kinetic friction. As shown below in the Physics Plus problem, the only difference between the two is the name given to the forces. 2) There are no units because it is a force divided by a force. 3)
Questions 1) The coefficient of friction from the first graph shows the friction between the floor and the wooden block as it was dragged. 2) My group's mew was 0.28 while the class averaged at 0.33, making the percentage difference 15.2%. Random and systematic errors account for the variation in everyone's results. 3) My percentage error was too high and my actual times were lower, which explained why we had a 15.2% error. Our group highest was 24.9% and the lowest was 18.9%. 4) The coefficient of friction is found in so many sports, like bowling or any sport involving running. Newton's Law acts in almost every activity we complete. 5)
The starting point from where I threw the ball might have not been lined up with the tape.
Because someone else
The block wasn't right next to the measurement, so I had to move it over a little bit to get an accurate measurement. The measurements are probably slightly off because of this.
What Do You Think Now? The surfaces that each sport is centered around require certain shoes for that specific reason. The shoes for each sport help give the athlete more or less friction, depending on what is necessary. Because sliding friction is not beneficial for athletes (it causes them to fall and injure themselves), the shoes need to decrease this to keep them up.
Physics To Go 1) For football, the spikes in their cleats allow them to gain traction from the turf. However, rain makes the turf slicker, requiring more friction. Some professional athletes change their cleats for ones that have harder spikes, giving them more friction than they would have gotten. 2) Bowlers want to have almost no friction from the floor in which they roll the ball down the lane. The friction would cause the ball to slow down, ergo the speed decreases and lessens the impact the ball inflicts onto the pins. 3) No because different courts may have been waxed at different periods of time or are made with different materials. A newly renovated court is going to be much more slippery than a older court that has been scuffed up. 4) Three different shoes would be needed for those courts. The grass court needs the most friction from the pair of shoes, while the hard surface court needs the least. The clay court is much smoother than a harder surface like cement, but more stable than grass; the shoes would need to have a medium type of friction.
5) Sigma(F) = ma N = W 600 N
mew = f/n .03 = f/600 f = 18 N
6A) w = mg w = 1000(9.8) w = 9800 N
6B) mew = f/n 0.55 = f/9800 f = 5390 N
6C) f(x) = ma(x) -5390 = 1000a a = -5.39 m/s^2
6D) vf = vi + at 0 = vi + (-5.39 x 6) 0 = vi - 32.34 vi = 32.34 m/s
6E) As shown from the equations above, the driver was moving at 32.34 m/s. However, he claimed to be driving at 29 m/s, 3.34 m/s less than the speed he was really driving. 7) Air resistance and water resistance are very important factors that change sliding friction. In most cases, they allow the object to move faster due to the lack of friction. A metal box is going to slide down a wet ramp faster than it would a dry one. Air resistance creates another force that allows an object to move or stay put, depending on its direction. 8) Maximum forces limit how fast someone is capable of moving, regardless of having "incredibly strong muscles". 9) Completed for extra credit 10) When you stand up, friction is what allows you to do so. When you are running, friction is needed to propel yourself forward and certain shoes increase or decrease the amount of friction. On grass, more friction is needed (like cleats for football), and on a track, less friction is needed. 11) Bryan Kist prepares to bowl his tenth strike in a row. Should he complete this, he will set a world record and be named the best bowler ever. Bryan eyes the pins and lines it up with the ball. Swiftly, he winds up and releases the ball with a sharp flick of the wrist. The ball glides across the lane, seemingly with no effort, but oh no the ball is curving to the left! The change in velocity alters its acceleration and the ball begins to slow down. The coefficient of friction has decreased! The ball hits the pins and... seven fall. Tragic, imaginary coanchor, just tragic.
Section 8
What Do You See? A girl is running towards a building using a pole vault to get on top of the 20 foot tall building.
What Do You Think? The doubling of the height may need to be equalized with a double amount of force. The pole in comparison to the force exerted on it may not be equal and therefore, someone would not be able to clear the 12 m high bar.
Investigation See Group Wiki
Physics Talk Joule: 1 N x m = 1(kg x m^2 / s^2) Kinetic Energy: energy associated with motion
KE = 1/2(m)(c^2)
Gravitational Potential Energy: the energy an object possesses because of its vertical position from Earth
GPE = mgh
Potential Energy: energy associated with position Law of Conservation of Energy: energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy remains constant Work: the product of the displacement and the force in the direction of the displacement
work = f x d
Elastic Potential Energy (Also Called Spring Potential Energy): the energy of a spring due to its compression or stretch
EPE = 1/2(k)(x^2)
Checking Up, p 227 1) For an object to move, work needs to be done. This is shown by work = force x distance. 2) The penny gets its energy from the ruler's energy as it moves down before snapping back into place, therefore transferring the energy into the penny to make it move. 3) By running, the person puts a force on the distance traveled. The person then acts like the penny because of the energy transfer between the person and the pole. 4) The units for all of those are joules, which is defined as 1 N x m = 1(kg x m^2 / s^2).
What Do You Think Now? Now that we know the formulas to determine if you can reach the height, the velocity in which you run changes the height. By doing so, the distance increases while the time decreases, but this cannot be done without increasing velocity. The kinetic energy increases when the elastic potential energy increases due to a variety of variables, such as making the pole a warmer temperature in order to increase flexibility.
Physics To Go 1) W --> KE --> GPE --> KE --> W
2) W --> KE --> GPE --> KE --> W
3) KE = GPE 1/2(m)(v^2) = mgh 1/2(v^2) = gh 1/2(v^2) = 9.8h 72 =9.8h h = 7.35 m
4) When pole vaulting, the person's mass and speed play significant roles besides the length of the pole.
5) When anything is warmer, it usually is more flexible, so the pole's flexibility would increase as well. When the system loses energy from the place of origin to the ending place, the energy goes into the environment as heat, as explained in the conservation of energy.
6) KE = w 1/2(m)(v^2) = mgh 1/2(v^2) = 9.8(4.55) (2)1/2(v^2) = 44.59(2) v^2 = 89.18 v = 9.4 m/s
7) 1/2(m)(v^2) = mgh 1/2(v^2) = gh 1/2(v^2) = 9.8(6.14) (2)1/2(v^2) = 60.172(2) v^2 = 120.34 v = 10.97 m/s
8A) GPE = KE 1/2(m)(v^2) = mgh 1/2(v^2) = 9.8(100) (2)1/2(v^2) = 980(2) v^2 = 1960 v = 44.27
8B) In this case, the mass of the rock is not calculated because it is cancelled out.
9A) EPE = w w = 1/2(k)(x^2) w = 1/2(1500)(0.25^2) w = 46.9
9B) EPE = KE 1/2(k)(x^2) = 1/2(m)(v^2) 1/2(1500)(0.25^2) = 1/2(0.1)(v^2) v = 30.6 m/s
10A) EPE = w fd = 1/2(k)(x^2) 30f = 1/2(315)(30^2) f = 4725 J
15) When the batter swings the bat, they are transferring the energy from the work onto the ball, which then moves with kinetic energy. The ball reaches its maximum height from the gravitational potential energy.
16) The Law of Conservation can be seen in softball, especially when the ball is pitched. The energy is transferred from work to kinetic energy, and once the ball is hit (like a pop up), the GPE acts on the ball. All of the energy forms are equal to one another.
Section 9
What Do You See? I see an ice skater jumping up in the air while twirling (hang time). A person in a helicopter is timing the ice skater.
What Do You Think? Certain sports allow the hang time to exceed gravity, because their momentum is so great going up in the air that allows them to execute the stunt, like during diving.
Investigation 20 frames, 1/30 second = 2/3 second
1) Bending the knees --> Unbending the knees --> Becoming airborne
2A) The amount of energy when unbending your knees. 2B) The data shown in #5 2C) Meter stick, force platform 2D) We ran trials by measuring each other's bend, jump, and distance.
3) Measurements:
Mass: 58.96 g
Weight: 577.87 g
Jump .12 m
Bend: .4 m
w = GPE fd = mgh .4f = (58.96)(9.8)(.12) f = 173.34 N
4) When I used the platform, my force was 300.4924 N
I'm surprised at my percentage error because of its smallness. It probably attributes to the fact that my numbers are all relatively smaller than someone like Jesse or Russell, ergo my percent error is small too.
Conclusion: This lab helped us explore where and how energy is converted, and that the higher you jump, the more force will be exerted onto the ground when you land.
My data is found in navy blue (run three)
Physics Talk
Energy
Position
Elastic Potential Energy
Gravitational Potential Energy (GPE)
Kinetic Energy = 1/2(m)(v^2)
Ready Position
Maximum
0
0
Launch Position
0
Some
Maximum
Peak Position
0
Maximum
0
Energy
Position
EPE
GPE = mgh
KE = 1/2(m)(v^2)
Ready Position
410 J
0
0
Launch Position
0
150 J
260 J
Peak Position
0
410 J
0
Energy Position
EPE
GPE
KE
Ready Position
600 J
0
0
Launch Position
0
150 J
450 J
Peak Position
0
600 J
0
Energy Position
EPE
GPE
KE
Ready Position
0
2300 J
0
Launch Position
0
500 J
1800 J
Peak Position
2300 J
0
0
Checking Up 1) The energy used in the work formula is described by the distance from the crouching position to the ready position. 2) When launched, kinetic and gravitational potential energies are used, and its maximum height is calculated with GPE. 3) Other types of energy include the following:
Chemical energy
Gravitational energy
Kinetic energy
Light energy
Nuclear energy
Work
Physics Plus, p242 1A) GPE = KE mgh = 1/2(m)(v^2) gh = 1/2(v^2) 9.8(20) = 1/2(v^2) v = 19.8 m/s
1B) The masses cancel out on either side of the equal sign, and it does not effect the velocity of which.
2) EPE + GPE = KE 1/2(k)(x^2) + mgh = 1/2(m)(v^2) 1/2(60)(0.4^2) + 0.3(9.8)(2) = 1/2(0.3)(v^2) v = 4.2 m/s
3) GPE + W = KE + GPE mgh + 150,000 = mgh (9.8)(25) + 150,000 = 9.8h h = 15,331.1 m
What Do You Think Now? Hang time is not defying gravity because everything in the air is acted upon GPE. After watching the video of the ice skater, you can see the maximum height and the displacement by marking their feet. Even a world-class figure skater can't defy gravity for too long, even if it appears so.
Physics To Go 1) w(in) = GPE = mgh = 50(9.8)(1) 490 J
2) W(in) + GPE --> KE --> W(out)
3) Just like how we recorded the ice skater's movement in the slow-motion clip, we would be able to do the same for the player's foot during each slide. Showing this would disprove the concept of hang time but that his maximum height is really displacement.
4) The person that thinks that the law of physics is not true they need to prove it. Because the law is something most scientists use, there is ample evidence that it exists. Breakthrough evidence has to be provided and replicated to verify that the theory is correct.
5) In order for an athlete, like a basketball star, to jump higher, they need to build up leg muscle or decreasing body mass. This way they are able to increase their force AND their jump.
6A) 1 J 6B) 10 J 6C) 10 J 6D) 10 J 6E) 10 J
7) The same amount of J 8) The same amount of J
9) F x d 50(43) = 2150 J
10) KE = 1/2(m)(v^2) KE = 1/2(62)(8.2^2) 2084.4 J
11A) F = ma 30 N = 5a a = 6 m/s^2
11B) W = Fd w = 30n(18.75) w = 562.5 J
12A) w = Fd 40,000 = 3200d d = 12.5 m
12B) F = ma 3200 = 1200a a = 2.67 m/s^2
13) KE = w 1/2m(v^2) = w 1/2(0.15)(40)^2 = w w = 120 J
14) w = KE Fd = 1/2(m)(v^2) 417d = 1/2(64)(15^2) d =17 J
Table of Contents
Section 1
Current Events
In this article, scientists have discovered that a competitor with two prosthetic lower legs are outrunning the competition because the prosthetics make him run "15-20% faster, equal to 10 seconds over a 400 meter race, than he otherwise would be with natural legs." The reason for this is because regular bone density weighs more than half of a prosthetic, which changes the runner's ability to run faster than someone with natural legs possibly can.
http://www.livescience.com/culture/091130-sports-pistorius-artificial-legs.html
What Do You See?
There is a kid in a red shirt running and kicking the ball over the goal. Another kid is standing still while kicking a ball, and it doesn't get enough momentum to get a good distance.
What Do You Think?
Once they begin to slide across the ice, they gain momentum and that keeps them at high speeds while no large effort is made to do so. The soccer ball that has been kicked across still has force and momentum, which keeps the acceleration going.
Investigate
2A) 5.25 m
2B) The skater will go back and forth but will gradually decrease his height as time goes goes on.
3A) The result was 6.03 m. The prediction wasn't completely off, but it was close. Also as time went on, the height of the skater did not decrease or increase.
3B) The ball remains constant in its maximum height.
4A) Our prediction is that, the maximum height of the ball will be less than its maximum height with a steeper slope. Measurement prediction: 5.50 m.
4B) The result is 5.08 m. Our prediction was very close because we predicted the maximum slope to be less than when it had a steep slope. The second result is 4.41 m. Still proving our prediction to be correct.
5A) No because there is no slope to give the skater the necessary momentum to bring him back to max height. He will simply fall of the slope.
5B) We predict it will take 100 m. for the skater to stop.
5C) The thing to keep the skater rolling on the track is to have absolutely no friction to allow him to stop.
5D) The skater does not stop rolling no matter how long the horizontal track is.
6A) The other side of the track is elongated.
6B) The max height also decreases with a less steep slope.
6C) They are usually about equal if the slope on each side is equal.
6D) The skate would not stop if there was a horizontal slope. If there was not a horizontal slope, he would go back in the other direction.
Physics Talk, p134-138
Inertia: the natural tendency of an object to remain at rest or to remain moving with constant speed.
Force: a push or a pull
Newton's First Law: in the absence of an unbalanced force, an object at rest remains at rest, and an object already in motion remains in motion with constant speed in a straight-line path.
Mass: the amount of matter in an object; how we measure inertia; measured in kilograms
Weight: how much gravity pulls on a mass
Speed: the charge in distance per unit of time
Velocity: speed in a given direction
Acceleration: the change in velocity per unit of time
Frame of Reference: a vantage point with respect to which position and motion may be described.
Checking Up, p138
What Do You Think Now?
Both the figure skater and soccer ball will continue to roll on a horizontal plane until the object reacts with friction. Their speed is determined by the amount of friction; both will lose their speed with more friction, and increase their speed with less friction. Theoretically, they can continue for ever if there was no friction to stop them.
Physics To Go, p143
1) It will never stop because there is no unbalanced force to do so.
2) It reaches the same height that it started with as long as there is no friction (20).
3) No because everything has at least a little but of friction.
4) The puck will glide at constant speed.
5) 2.5 m/s + 4.5 m/s = 7 m/s
6) 4.2 m/s + 10.3 m/s = 14.5 m/s
7A) 5.6 m/s + 2.4 m/s = 8 m/s forward
7B) 5.6 m/s - 2.4 m/s = 3.2 m/s forward
7C) 5.6^2 + 2.4^2 = c^2
[square it]
6.1 m/s at 67 degrees, 23 degrees from train direction
8) 85 m/s - 18 m/s = 67 m/s
9A) 21.2 cm
9B) 43.9 cm
9C) 58 cm
9D) 172 cm
10) Bowling, punting a football, and a basketball use Newton's First Law because the ball will stop rolling at some point because outside forces are influencing it. The ball will keep rolling unless it acts against a surface with friction.
Inquiring Further
Most baseball players need to beat out the ball to get to first base, and they can run through the base. However, overrunning the base allows the runner to get tagged and be out, so they need to slide and react with the friction of the ground to stop before they overrun the base.
Section 2
What Do You See?
In the top section of the picture, the boy is walking slowly and is footprints are closer together; at the bottom half, he is sprinting after a girl with flowers in tow, and his footprints are much further apart.
What Do You Think?
The meaning of 100 mi/h = 45 m/s. The number for distance is significantly less because of the conversion between miles and meters, and hours and seconds.
Investigate
See group wiki
Physics Talk, p148-151
Acceleration: a change in velocity of an object over time
- a = delta v / delta t
Average Speed: the distance traveled divided by the time it took to travel that distance- v(av) = delta d / delta t
Instantaneous Speed: the speed measured during an instant: the speed as the time interval approaches, but does not become zero.Checking Up, p151
1A) The dots have a constant pattern and similar separation between each dot.
1B) The dots start out close together and then begin to grow apart in distance
1C) The dots start out further apart and move closer together.
2) 400m / 50s = 8 m/s
3) Instantaneous speed is the speed one is traveling at that exact time, compared to average speed which is the average speed over the course of a period of time.
4) v = 3.6 km/s , t = 10 s
3.6 / 10 = .36 km/s
Physics Plus, p152
1)
*rebounding (any object)
2) a = vf - vi / t
-.5 m/s - .5 m/s/ .2 s
a = -5
3A) .5 m/s
3B) -0.5 m/s
3C) .5 m/s
What Do You Think Now, p152
The miles still need to be converted into meters, as well as changing the hours to correspond with seconds, which is converted into 89.7 m/s. Distances traveled in comparison to time usually go hand in hand. In this example, every hour 100 miles have been completed, compared to 45 m/s, which is 45 meters per one second. By an hour, 162,000 meters will have been covered.
Physics To Go, p154-156
1) Average speed
2A) 60 m/s
2B) 14 m/s
2C) 4.8 km/h
2D) 89 km/h
3A) negative acceleration
3B) positive acceleration
3C) constant speed
3D) negative
3E) constant speed
3F) constant speed
4A) A & D
4B) B
4C) A
4D) C
4E)
6A) a = vf - vi / t
0-12.5 m/s / 9 s = -1.4 m/s
6B) negative
7A) Constant
7B) Increasing
7C) Constant, Increasing, Constant
7D) Increasing, Decreasing, Increasing
8) 100 m / 2 h = 50 mph
9) No because the speed will almost never be maintained. They may have walked very fast for the first few blocks and slower for the rest.
10) See chart
11) 4 m/s x 5 s = 20 m/s
14A) When running track, you are in constant motion but your speed may begin to vary the longer you're running for.
14B) When pitching a softball, you wind up to get the ball to move faster in order for it to constantly accelerate at a fast speed.
14C) When bowling, the ball is moving pretty slowly at a constant speed.
14D) When running to pole vault, you need to have a running start before putting the pole down to ensure that you go straight up in the air.
14E) When running to 2nd base, you need to slow down in order to not overrun the base.
Section 3
What Do You See?
The girl is walking with a red stick, pushing a blue ball. When she increases her speed, it's difficult for her to continue to push the ball because she is hindered by the red stick's friction to he ground. The more she pushes, the higher she goes.
What Do You Think?
Force is a push or a pull exerted onto an object. A tennis ball will have more force exerted onto it than a bowling ball based on its smaller mass, which allows the tennis ball to move further away than the bowling ball at a faster speed.
Investigation
See Group Wiki
Physics Talk, p161-167
Free-Body Diagram: a diagram showing the forces acting on an object
Weight: the vertical, downward force exerted on a mass as a result of gravity
Equation for Newton's Seond Law of Motion
Class Notes
With an unbalanced force, an object will acclerate.
Newton's Second Law: Net force is directly proportional to acceleration.
Gravity = 9.8 m/s^2
A big force causes a big acceleration; a small force causes a small acceleration.
A big mass needs a big force to accelerate; a small mass needs a small force to accelerate
Net force has NO RELATIONSHIP to velocity
Checking Up, p167
1) Newton's Second Law: Net force is directly proportional to acceleration
2) The acceleration will be increasing even with a constant force.
3) You would need to work backwards to find how much it weighs in pounds:
weight in N = mg (x kg) x 9.8 = 30 N
x = 3.06 kg
y lbs
_ = 3.06 kg
2.2 kg
y = 6.732 lbs
z = 30 N
4) Your mass will remain the same, but your weight would change because of the gravitational force that your body has on that planet.
Physics Plus, p169
What Do You Think Now, p170
After finishing the Investigation, now I know the exact formula for calculating force in association with mass and acceleration. Due to Newton's Second Law, force is exerted onto an object, and a greater mass increases its speed.
Physics to Go, p171-173
1)
3)
a = ?
m = .3 kg
F = 42 N
42 N = (.3 kg) a
a = 140 m/s^2
4)
f = ?
m = .04 kg
a = 20 m/s^2
f = (.04 kg) 20 m/s^2
f = .8 N
5A) The bowling ball has a greater mass and therefore a greater inertia, making it much more difficult to stop, unlike the baseball.
5B) The bowling ball and the baseball have the same force but the acceleration differs due to their mass.
9) Once the ball is released from your hand, there is no force acting on the ball except its acceleration.
10) 90 N
11) 4 x 200 = 800 N
12) 179 m/s^2
13) 130 N @ 67 degrees NE
14) 6403 N @ 39 degrees
15) 125 N
16A) 50 N @ 53 degrees
16B) 8.9 m/s^2
17A) 36 N @ 34
17B) .36 m/s^2
17C) .5 m/s^2
18) Welcome to the Pascack Hills Volleyball State Tournament Finals! The home team, Pascack Hills, seed 4, is playing against the number one seed, Old Tappan. Aiyana Whitney smashes the ball down at a velocity of 2.5 m/s. Her 6 foot 3 inch stature gives the spike an edge, yet libero Keira Eichenlaub manages to put the ball back up. Sam Kurtzke, the setter, sprints to the ball to set it up to Jess Holm. Taking her approach, Holm sets herself up to increase her velocity to impact upon the ball, and her arm swing gives more speed to the balls initial velocity. The OT girls react too late, and Pascack Hills wins the point!
Section 4
What Do You See?
A girl is on a ladder dropping a red apple in free-fall, and the green apple is projecting. The two headed guy is timing both apples.
What Do You Think?
Both weight and velocity affect how far a thrown object travels.
Investigation
See Group Wiki (Group III)
Physics Talk
Trajectory: path
Projectile: an object acted on ONLY by gravity
Checking Up
1) They dropped at the same height, and acceleration is acting on both of them.
2) It increases about 10 meters every second
3) Velocity is 0 m/s; Acceleration is -9.8 m/s^2
Physics Plus, p179
1)
2)

What Do You Think Now?
After completing the Investigation, I now know that the height of the ball, the speed at which the ball is thrown, and the angle at which the ball is thrown affects the distance.
Physics To Go
1-2)
4) d=1/2at^2
6) This is true because the x and y components are independent; vertical distance is only affected by verticals, and horizontal distance is affected by horizontals.
7) Both of them hit the ground at the same time because the vertical component is the same but not the horizontal.
8) 36 @ 33.7 degrees
9A) 11.98 m/s
9B) v=d/t
11.3=d/t
d=23.96
10A) 8.5 m/s
10B) 4.25 m/s
11) Sammi Panso steps up to the plate, preparing for the fury Meredith Hryzck is about to release from the pitcher's mound. Hryzck winds up windmill style, and wow! Look at that! 80 miles an hour! The ball is spinning so much yet moving seamlessly on an imaginary horizontal plane; there's not way Panso will get this one. BAM! Gee whiz, that ball is really flying. And off she runs! (That's sure going to be at least a double, Amanda.) That's right imaginary co-anchor, the ball had some great arc on it; let's see if center fielder Ashley Worthington can manage to catch it. (Amanda, that ball is arced a little too much; I think Worthington is going to be able to catch it.) The ball is coming back to Earth now at an acceleration of -9.8 m/s^2, and Worthington is running back and back... AND SHE DIVES FOR THE BALL! Is it a catch, YES WE HAVE A CATCH. That was some play, Imaginary Co-Anchor, some play. And that's the game!
In this video, we see the players going up for spikes during their volleyball warmup. The ball is tossed up, with an initial acceleration of 0, and once it reaches its highest point, it accelerates at -9.8 m/s^2. Once the ball hits that point, the player begins their approach. This vertical motion of the ball is off set by the swinging of the arm, at which point the ball has no choice to go down. However, when the timing is off, the ball will be hit and move on a horizontal plane. The shape of the trajectory once the ball is spiked allows the opposing players to have a harder time digging the ball. If they fail to do so, the offensive team wins a point, helping them secure a win.
http://www.youtube.com/watch?v=rP2_4P0gMXk
Section 5
What Do You See?
A girl is kicking the ball backwards, and the ball is brought back down only to be hit off of number 2's head into the goal.
What Do You Think?
Depending on the angle that the ball is kicked at, it will reach a maximum of various heights and distances along the x and y axis. If the projectile is kicked harder, the force exerted onto the object
Investigation
See Group Wiki
Physics Talk, p188-189
Checking Up, p189
1) Horizontal motion and vertical motion are the two types of motion that show the trajectory of a projectile.
2) The model must match reality in nature, which means that the model must be backed up by science as well as show the physicality of the nature being shown.
3) Because ten degrees and 80 degrees are complimentary, they will yield the same distance. The ten degree launch will have a longer horizontal velocity than the eighty degree launch, but the latter will have a much higher vertical velocity.
Physics Plus, p192
What Do You Think Now?
The angles of the trajectory affect the projectile and where it moves to. When the angle is close to 45 degrees, the range is greater than if it were further away. Sometimes a projectile can be launched from a different angle yet yield the same range; angles that are complimentary (total 90 degrees) have the same range.
Physics To Go, 194-195
1) If the angles have the same range, then the angles must be complimentary. For the furthest distance, both angles must each total 45 degrees.
2A) The vertical distance will increase while the horizontal distance will decrease.
2B) The horizontal distance will increase while the vertical distance will decrease.
3A) 30 degrees & 60 degrees
3B) 15 degrees & 75 degrees
4) v(ix) > v(iy)
0 < 45 degrees
5) v(ix) is high and his maximum horizontal range is high.
6A) a = -g = -9.8 m/s down
6B) v(max) = v(ix)
v(y) = 0 at maximum height
7A) 29.4 m/s
7B) 5 m/s
7C) 15 m/s
8) Closest to forty five degrees
9) Biggest angle, the one closest to ninety degrees
10A) Down'
10B)
d = v(i) + 1/2at^2
-100 = .5 (-9.8) t^2
-200 / -9.8 = 4.5 s
10C)
d(x) = v(ix)t
d = 20 x 4.5
90 m
Section 6
What Do You See?
A boy looks like he is pushing against the wall as if to move it with all his might, but then he is propelled backwards.
What Do You Think?
They should bend their knees and push their feet into the ground, before propelling themselves upward. Gravity is pulling you down while Normal forces propel you upward.
Investigation
Part A
1A) The moment force is applied.
1B) When acceleration is equal to zero, there is no unbalanced force acting upon it.
1C) The force is a push which acts in the opposite direction of where you are moving.
1D) You push in the opposite direction on the wall.
1E) Both of them are equal in magnitude because if they weren't the wall would move to push you or you would go through the wall.
2A) Student A pushes forward and moves backwards.
2B) The force of the student's hands against the other student's hands causes the motion to propel backwards.
2C) The motion of the hands of students A & B are of equal force, causing the same motion
2D) The force of the student's hands against the other student's hands causes the motion to propel backwards.
3A) The forward forces comes from the backward force of each step of the show pushing off from the floor.
3B) It is possible but because of the lack of friction, more force must be applied to each step.
4A) The force will always be equal because they have the same mass and force, only in opposite directions.
4B)
Part B
3A) The more mass that rests on the ruler creates a greater bend.
4A) With each Newton of force, there is a greater deflection in the meter stick.
4B) The deflection is greater when the weight is greater.
4C) The stick is still deflecting, but at such a small angle it cannot be seen.
4D)
Physics Talk, p201
Newton's Third Law of Motion: Forces come in pairs; the force of object A on object B is equal in strength and opposite in direction to the force of object B on object A.
Free-Body Diagram: a diagram showing the forces acting on an object
Center of Mass: the point at which all the mass of an object is considered to be concentrated.
Class Notes:
1) An object at rest will stay at rest, and an object in motion will stay in motion at constant speed in a straight line, unless an unbalanced force acts upon it.
2) Acceleration is directly proportional to net force and inversely proportional to the mass of the system.
3) Every action has an equal but opposite force.
Checking Up, p205
1) When two objects have equal force is opposite directions.
2) Gravity and Normal forces act against each other.
3) The free-body diagrams illustrate where each force is moving in comparison to an object.
Physics Plus

Physics To Go, p208
1) Yes but it is equal to the opposite.
2) No but restoring forces balance weight downward.
3) A spring with a needle attached, calibrated.
4) Equal but opposite break because the force of the ball is too big for material to withstand.
5) Equal but opposite. The smaller running back has a larger acceleration but exerts the same force.
6) The forces are equal and opposite.
7) Padding causes lower acceleration which reduces force on hand.
8A) Mark Sanchez is waiting for the snap and oh no, the play clock is running out! One second left... the ball is snapped just in time. The linebackers slam into each other, exerting their own force upon their opponent. Newton's Third Law is at play, as you can see the line is not moving; equal forces are coming from both sides of the field. Meanwhile, Sanchez is looking for Dustin Keller, fakes, and bombs it to Braylon Edwards. Look at that throw, but oh no! It's too high! Edwards jumps up, catches it in mid air, and falls into the N-Zone. TOUCHDOWN NEW YORK!
8B) Deflection on the ground causes force because when an object hits the ground at one force, it will deflect with the same amount of force.
What Do You Think Now?
You are pushing your weight down upon the floor, while normal forces are pushing upward. The normal forces of both yourself and the floor are equal, which allows you to spring upward.
Section 7
What Do You See?
The person is pulling a shoe across the ice easily with a spring scale, but is having difficulty doing so on the sand.
What Do You Think?
Certain shoes like cleats have spikes that stick into the sand or grass or turf, allowing for more traction. Athletes that wear them need to stay up while running, and the spikes allow them to do so. Other shoes like volleyball and basketball sneakers are meant so the athletes won't slip on the court and injure themselves.
Investigation 2-7
See Group Wiki
Physics Talk, p212
Friction: a force that resists relative motion between two bodies in contact
Normal Force: the force acting perpendicularly or at right angles to a surface.
Coefficient of sliding friction: a dimensionless quality symbolized by the Greek letter (meu); its value depends on the properties of the two surfaces in contact and is used to calculate the force of friction.
Checking Up, p214
1) They are both equal forces because on is sliding friction and the other is kinetic friction. As shown below in the Physics Plus problem, the only difference between the two is the name given to the forces.
2) There are no units because it is a force divided by a force.
3)
Physics Plus, p215
Bowling Blocks Lab
(N)
f = max
.46=.17a
a = 2.7(m/s)^2
Sigma(y) = ma(y)
N-W=0
N=W
W=(.17)(9.8)
W = 1.66N
Mew = f/N
.28 = f/1.66
f = .46N
Vf^2 = Vi^2 +2ad
Vi^2 = -24.84
0=Vi^2+2(-2.7)(4.6)
Vi = 5
Vf = Vi + at
0 = 5 + 2(-2.7)t
t = 1.85
Questions
1) The coefficient of friction from the first graph shows the friction between the floor and the wooden block as it was dragged.
2) My group's mew was 0.28 while the class averaged at 0.33, making the percentage difference 15.2%. Random and systematic errors account for the variation in everyone's results.
3) My percentage error was too high and my actual times were lower, which explained why we had a 15.2% error. Our group highest was 24.9% and the lowest was 18.9%.
4) The coefficient of friction is found in so many sports, like bowling or any sport involving running. Newton's Law acts in almost every activity we complete.
5)
What Do You Think Now?
The surfaces that each sport is centered around require certain shoes for that specific reason. The shoes for each sport help give the athlete more or less friction, depending on what is necessary. Because sliding friction is not beneficial for athletes (it causes them to fall and injure themselves), the shoes need to decrease this to keep them up.
Physics To Go
1) For football, the spikes in their cleats allow them to gain traction from the turf. However, rain makes the turf slicker, requiring more friction. Some professional athletes change their cleats for ones that have harder spikes, giving them more friction than they would have gotten.
2) Bowlers want to have almost no friction from the floor in which they roll the ball down the lane. The friction would cause the ball to slow down, ergo the speed decreases and lessens the impact the ball inflicts onto the pins.
3) No because different courts may have been waxed at different periods of time or are made with different materials. A newly renovated court is going to be much more slippery than a older court that has been scuffed up.
4) Three different shoes would be needed for those courts. The grass court needs the most friction from the pair of shoes, while the hard surface court needs the least. The clay court is much smoother than a harder surface like cement, but more stable than grass; the shoes would need to have a medium type of friction.
5) Sigma(F) = ma
N = W
600 N
mew = f/n
.03 = f/600
f = 18 N
6A) w = mg
w = 1000(9.8)
w = 9800 N
6B) mew = f/n
0.55 = f/9800
f = 5390 N
6C) f(x) = ma(x)
-5390 = 1000a
a = -5.39 m/s^2
6D) vf = vi + at
0 = vi + (-5.39 x 6)
0 = vi - 32.34
vi = 32.34 m/s
6E) As shown from the equations above, the driver was moving at 32.34 m/s. However, he claimed to be driving at 29 m/s, 3.34 m/s less than the speed he was really driving.
7) Air resistance and water resistance are very important factors that change sliding friction. In most cases, they allow the object to move faster due to the lack of friction. A metal box is going to slide down a wet ramp faster than it would a dry one. Air resistance creates another force that allows an object to move or stay put, depending on its direction.
8) Maximum forces limit how fast someone is capable of moving, regardless of having "incredibly strong muscles".
9) Completed for extra credit
10) When you stand up, friction is what allows you to do so. When you are running, friction is needed to propel yourself forward and certain shoes increase or decrease the amount of friction. On grass, more friction is needed (like cleats for football), and on a track, less friction is needed.
11) Bryan Kist prepares to bowl his tenth strike in a row. Should he complete this, he will set a world record and be named the best bowler ever. Bryan eyes the pins and lines it up with the ball. Swiftly, he winds up and releases the ball with a sharp flick of the wrist. The ball glides across the lane, seemingly with no effort, but oh no the ball is curving to the left! The change in velocity alters its acceleration and the ball begins to slow down. The coefficient of friction has decreased! The ball hits the pins and... seven fall. Tragic, imaginary coanchor, just tragic.
Section 8
What Do You See?
A girl is running towards a building using a pole vault to get on top of the 20 foot tall building.
What Do You Think?
The doubling of the height may need to be equalized with a double amount of force. The pole in comparison to the force exerted on it may not be equal and therefore, someone would not be able to clear the 12 m high bar.
Investigation
See Group Wiki
Physics Talk
Joule: 1 N x m = 1(kg x m^2 / s^2)
Kinetic Energy: energy associated with motion
- KE = 1/2(m)(c^2)
Gravitational Potential Energy: the energy an object possesses because of its vertical position from Earth- GPE = mgh
Potential Energy: energy associated with positionLaw of Conservation of Energy: energy cannot be created or destroyed; it can be transformed from one form to another, but the total amount of energy remains constant
Work: the product of the displacement and the force in the direction of the displacement
- work = f x d
Elastic Potential Energy (Also Called Spring Potential Energy): the energy of a spring due to its compression or stretchChecking Up, p 227
1) For an object to move, work needs to be done. This is shown by work = force x distance.
2) The penny gets its energy from the ruler's energy as it moves down before snapping back into place, therefore transferring the energy into the penny to make it move.
3) By running, the person puts a force on the distance traveled. The person then acts like the penny because of the energy transfer between the person and the pole.
4) The units for all of those are joules, which is defined as 1 N x m = 1(kg x m^2 / s^2).
What Do You Think Now?
Now that we know the formulas to determine if you can reach the height, the velocity in which you run changes the height. By doing so, the distance increases while the time decreases, but this cannot be done without increasing velocity. The kinetic energy increases when the elastic potential energy increases due to a variety of variables, such as making the pole a warmer temperature in order to increase flexibility.
Physics To Go
1) W --> KE --> GPE --> KE --> W
2) W --> KE --> GPE --> KE --> W
3) KE = GPE
1/2(m)(v^2) = mgh
1/2(v^2) = gh
1/2(v^2) = 9.8h
72 =9.8h
h = 7.35 m
4) When pole vaulting, the person's mass and speed play significant roles besides the length of the pole.
5) When anything is warmer, it usually is more flexible, so the pole's flexibility would increase as well. When the system loses energy from the place of origin to the ending place, the energy goes into the environment as heat, as explained in the conservation of energy.
6) KE = w
1/2(m)(v^2) = mgh
1/2(v^2) = 9.8(4.55)
(2)1/2(v^2) = 44.59(2)
v^2 = 89.18
v = 9.4 m/s
7) 1/2(m)(v^2) = mgh
1/2(v^2) = gh
1/2(v^2) = 9.8(6.14)
(2)1/2(v^2) = 60.172(2)
v^2 = 120.34
v = 10.97 m/s
8A) GPE = KE
1/2(m)(v^2) = mgh
1/2(v^2) = 9.8(100)
(2)1/2(v^2) = 980(2)
v^2 = 1960
v = 44.27
8B) In this case, the mass of the rock is not calculated because it is cancelled out.
9A) EPE = w
w = 1/2(k)(x^2)
w = 1/2(1500)(0.25^2)
w = 46.9
9B) EPE = KE
1/2(k)(x^2) = 1/2(m)(v^2)
1/2(1500)(0.25^2) = 1/2(0.1)(v^2)
v = 30.6 m/s
10A) EPE = w
fd = 1/2(k)(x^2)
30f = 1/2(315)(30^2)
f = 4725 J
10B) 4725 J
11) GPE = EPE
mgh = 1/2(k)(x^2)
(0.04)(9.8)(1) = 1/2(18)(x^2)
x = 0.21
12A) F = ma
N = kg(m/s^2)
W = Fd
J = Nm
12B) GPE = mgh
GPE = kg (m/s^2) (m)
GPE = N(m)
GPE = J
12C) KE = 1/2mv^2
KE = kg (m/s)^2
KE = kgm/s^2 (m)
KE = N(m)
KE = J
12D) EPE = 1/2kx^2
EPE = N/m (m^2)
EPE = N(m)
EPE = J
13) EPE --> KE --> GPE
14) EPE --> w --> KE --> GPE
15) When the batter swings the bat, they are transferring the energy from the work onto the ball, which then moves with kinetic energy. The ball reaches its maximum height from the gravitational potential energy.
16) The Law of Conservation can be seen in softball, especially when the ball is pitched. The energy is transferred from work to kinetic energy, and once the ball is hit (like a pop up), the GPE acts on the ball. All of the energy forms are equal to one another.
Section 9
What Do You See?
I see an ice skater jumping up in the air while twirling (hang time). A person in a helicopter is timing the ice skater.
What Do You Think?
Certain sports allow the hang time to exceed gravity, because their momentum is so great going up in the air that allows them to execute the stunt, like during diving.
Investigation
20 frames, 1/30 second = 2/3 second
1) Bending the knees --> Unbending the knees --> Becoming airborne
2A) The amount of energy when unbending your knees.
2B) The data shown in #5
2C) Meter stick, force platform
2D) We ran trials by measuring each other's bend, jump, and distance.
3) Measurements:
- Mass: 58.96 g
- Weight: 577.87 g
- Jump .12 m
- Bend: .4 m
w = GPEfd = mgh
.4f = (58.96)(9.8)(.12)
f = 173.34 N
4) When I used the platform, my force was 300.4924 N
5) %error = | calc - exp | / calc x 100
%error = | 173.34 - 300.4924 | / calc x 100
%error = |-127.15| / 173.34 x 100
%error = 127.12 / 17334
% error = 0.007
I'm surprised at my percentage error because of its smallness. It probably attributes to the fact that my numbers are all relatively smaller than someone like Jesse or Russell, ergo my percent error is small too.
Conclusion: This lab helped us explore where and how energy is converted, and that the higher you jump, the more force will be exerted onto the ground when you land.
My data is found in navy blue (run three)
Physics Talk
Position
Position
Position
Position
Checking Up
1) The energy used in the work formula is described by the distance from the crouching position to the ready position.
2) When launched, kinetic and gravitational potential energies are used, and its maximum height is calculated with GPE.
3) Other types of energy include the following:
Physics Plus, p242
1A) GPE = KE
mgh = 1/2(m)(v^2)
gh = 1/2(v^2)
9.8(20) = 1/2(v^2)
v = 19.8 m/s
1B) The masses cancel out on either side of the equal sign, and it does not effect the velocity of which.
2) EPE + GPE = KE
1/2(k)(x^2) + mgh = 1/2(m)(v^2)
1/2(60)(0.4^2) + 0.3(9.8)(2) = 1/2(0.3)(v^2)
v = 4.2 m/s
3) GPE + W = KE + GPE
mgh + 150,000 = mgh
(9.8)(25) + 150,000 = 9.8h
h = 15,331.1 m
What Do You Think Now?
Hang time is not defying gravity because everything in the air is acted upon GPE. After watching the video of the ice skater, you can see the maximum height and the displacement by marking their feet. Even a world-class figure skater can't defy gravity for too long, even if it appears so.
Physics To Go
1) w(in) = GPE = mgh
= 50(9.8)(1)
490 J
2) W(in) + GPE --> KE --> W(out)
3) Just like how we recorded the ice skater's movement in the slow-motion clip, we would be able to do the same for the player's foot during each slide. Showing this would disprove the concept of hang time but that his maximum height is really displacement.
4) The person that thinks that the law of physics is not true they need to prove it. Because the law is something most scientists use, there is ample evidence that it exists. Breakthrough evidence has to be provided and replicated to verify that the theory is correct.
5) In order for an athlete, like a basketball star, to jump higher, they need to build up leg muscle or decreasing body mass. This way they are able to increase their force AND their jump.
6A) 1 J
6B) 10 J
6C) 10 J
6D) 10 J
6E) 10 J
7) The same amount of J
8) The same amount of J
9) F x d
50(43) = 2150 J
10) KE = 1/2(m)(v^2)
KE = 1/2(62)(8.2^2)
2084.4 J
11A) F = ma
30 N = 5a
a = 6 m/s^2
11B) W = Fd
w = 30n(18.75)
w = 562.5 J
12A) w = Fd
40,000 = 3200d
d = 12.5 m
12B) F = ma
3200 = 1200a
a = 2.67 m/s^2
13) KE = w
1/2m(v^2) = w
1/2(0.15)(40)^2 = w
w = 120 J
14) w = KE
Fd = 1/2(m)(v^2)
417d = 1/2(64)(15^2)
d = 17 J
15)